The present invention relates to an optical illumination and imaging system for a reproduction device and, and more particularly, to a flash exposure system which utilizes a wide-angle, fixed lens and an integrating cavity light housing having a movable platen and floor arrangement to enable reduction and enlargement modes of operation.
Imaging systems which produce reduced or enlarged document images using conventional scanning optics are known in the art. A machine currently sold by the Minolta Co. called the "Minolta EP 710" utilizes an optical system which has a variable scan speed coordinated to the movement of the projection lens. The lens is translated towards or away from the imaging surface with the scanning speed and folding mirror position adjusted to maintain correct object-to-image distances. A disadvantage with this type of prior art system wherein a stationary document is scanned, typically by a moving lamp/mirror arrangement, is that output limitations are imposed by the scan and return-to-scan time requirements. As demands for faster copying and duplicating have increased, these conventional machines which scan documents in incremental fashion to provide a flowing image on a xerographic drum have proved inadequate. New high speed techniques have evolved which utilize flash exposure of an entire document (full-frame exposure) and the arrangement of a moving photoconductor in a flat condition at the instant of exposure.
One example of a high speed, multi-magnification machine is the Xerox 9200 copier/duplicator. This machine utilizes a flash illumination system wherein a relatively narrow half angle (.about.17.degree.) lens projects a document image along a folded optical path onto a flat photoreceptor. Besides the 1X reproduction mode, the 9200 has reduction modes in which the lens is translated towards the imaging plane and a plurality of add-lenses are moved into the optical path to maintain proper focus.
Another example of a full-frame flash system having reduction capabilities is that disclosed in U.S. Pat. No. 4,116,554. In this system, a magnification capability is enabled by utilizing a combined lens and mirror translation.
In copending U.S. Application Ser. No. 372,581, a full-frame flash system is disclosed wherein a reduction capability is enabled by translating the document platen away from the lens while the lens is simultaneously moved towards the image plane.
Heretofore, a flask exposure system having both reduction and enlargement capabilities, has not been realized although the advantages thereof are readily apparent. The problems which must be solved in enabling a multi-magnification flash system including maintaining an adequate illumination level at the document platen over all modes of operation and maintaining required document-to-photoreceptor distances during movement of the projection lens. Applicants have solved these problems by providing a simple compact "straight through" system (e.g. no folding mirrors), and have set the projection lens in a movable floor of a light housing. A portion of the platen housing wall, having an illumination lamp secured thereto, is also movable in conjunction with the floor/lens movement, the combined movement adapted to provide required image magnification at the photoreceptor while yet maintaining total object-to-image conjugate and document corner registration. The imaging system provides a continuous magnification capability of 0.647X through 1.55X while according to the present invention, maintaining corner registration of the document to be copied.
More particularly the invention is directed to an imaging system for providing, at an image plane, reduced or enlarged images of a document lying in an object plane comprising:
an enclosed light housing which includes a vertically translatable transparent platen assembly forming the top surface thereof and a vertically translatable floor assembly forming the bottom surface thereof,
a projection lens mounted in an aperture of said floor assembly,
means for simultaneously changing the position of said platen assembly and said floor assembly in response to a particular magnification selection,
flash illumination means within said housing to provide substantially uniform illumination of said platen; and
lens registration means for providing a horizontal component of motion to said lens simultaneously with said vertical lens movement to maintain corner registration of said document at the imaging plane.